WO1993001228A1

WO1993001228A1 - U.v. stabilizer composition for surface modifying a pvc resinous sheet

Info

Publication number: WO1993001228A1
Application number: PCT/US1991/004774
Authority: WO
Inventors: Neal D. Conrad; Joseph Silbermann; Michael T. Burchill
Original assignee: Atochem North America Inc
Current assignee: Arkema Inc
Priority date: 1988-08-26
Filing date: 1991-07-10
Publication date: 1993-01-21
Anticipated expiration: 1994-01-10

Abstract

A U.V. stabilizer composition having a PVC resin-swellable organic solvent and a U.V. stabilizer present in the solvent. The U.V. stabilizer is present in a concentration of at least 18 wt % and effective to incorporate in the PVC resin at ambient temperature an amount of UV stabilizer effective to stabilize the surface of the PVC resin.

Description

Description U.V. STABILIZER COMPOSITION FOR SURFACE MODIFYING A PVC RESINOUS SHEET

Technical Field

This invention relates to a PVC resinous article having its surface modified with a U.V. stabilizer, and, more particularly, to a U.V. stabilizer composition which is particularly effective for surface modification of PVC resinous articles. Background Art

Photodegradation of many types of solid polymeric articles by U.V. light has been a continual problem confronting the industry. Such U.V. degradation causes discoloration, embrittlement and deterioration of the article. Accordingly, U.V. absorber compounds have been incorporated into such polymeric articles in an attempt to provide effective stabilization to U.V. light.

However, photodegradation is known to be a surface phenomenon. Accordingly, incorporation of U.V. stabilizers into the polymeric material prior to shaping the resin into solid form has been largely uneconomical and inefficient because the stabilizer is present substantially in the interior of the shaped article, where it cannot function effectively to prevent surface photodegradation.

Accordingly, surface treatments have been proposed to provide more effective U.V. protection for resins such as PVC. These surface treatments are based on the ability of various organic solvents to swell the resin and to direct the ultraviolet light stabilizer material dissolved in the solvent principally into the surface region of the resin body.

The swelling method is described in detail, for example, by Katz, et al. in articles appearing in the "Proceedings of the A.S.C. Div. of Org. Coatings and Plastics" .36., (1) P- 202-205 (1976), entitled "Ultraviolet Protection of Transparent PVC by Diffusion Coating; and in Soc. Plast. Eng., Tech. Papers (1976), .22., 511-512. Katz uses a dip method to impregnate a transparent PVC sheet with a non-migrating ultraviolet light absorber. The dip technique comprises swelling the polymer with a carrier solvent, infusing the stabilizer from dilute solution, e.g. 3-6.5% by wt. of stabilizer in the carrier, and thereafter heating the treated polymer in air at an elevated temperature to drive the stabilizer below the surface of the polymer and to remove residual solvent. The solvents disclosed were toluene, tetrachloroethane, chloroform and 1,2- dichloroethane, and mixtures of chloroform and 1,2- dichloroethane.

Jochanan, in Israel Patent No. 39,037, published Nov. 10, 1975, entitled "U.V.-and Oxidation-Proof Products from Organic Plastics and their Manufacture", describes various methods of applying a 5% by wt. solution or suspension of an ultraviolet light absorber in methylene chloride to the surface of a plastic sheet. The methods disclosed by Jochanan included immersion, spraying, brushing, roller-printing and curtain-coating. However, with such application methods, a large method amount of residual stabilizer and solvent is left on the surface of the article, whereupon the modified surface is observed to be streaky, hazy, and has runs or pockmarks thereon. In fact, at a stabilizer concentration of 12.5% by wt., the resultant surface was found to become white and opaque.

Amborski, in U.S. 3,043,709, discloses an organic polymeric article having an ultraviolet light absorber compound adjacent to the surface of the article. The article is treated by several methods, including dipping-coating a PVC film in a 2 1/2% by wt. stabilizer solution in ethanol, and, thereafter, heating the coated film in air at 130°C. to drive the absorber below the surface of the film and to remove the solvent. Ethanol, however, is a very poor swelling solvent for PVC, and little or no incorporation of stabilizer is observed.

Solvay and Cie, in Belgian Patent No. 612,206, discloses a process for surface treating rigid polyvinyl chloride objects. The method comprises immersing the object in a swelling solvent containing a very small amount of light stabilizer, e.g. a 0.5% by wt. solution, and then evaporating the solvent in air. The solvents disclosed are THF, cyclohexanone, DMF, acetone and carbon disulfide.

Bristol, in U.S. 3,519,462, describes the treatment of polyvinyl chloride and other polymers with a solution of a U.V. stabilizer in a diol or triol, e.g. propylene glycol. These solvents, however, are not efficient swelling agents for PVC.

Lempkowicz, in U.S. Patent 4,126,600, describes a solution process surface modifying PVC sheets by applying a stabilizer solution in air to a PVC sheet heated to 120°C. (Example 1) and then vaporizing the solvent remaining in the sheet. The amount of U.V. agent present in the treatment solution is disclosed to vary between 5 and 40% by weight of the solution, preferably between 10 and 30% by wt. Suitable solvents are disclosed as being chlorinated solvents derived from hydrocarbons from 1 to 3 carbon atoms. However, according to the description and examples, the solvent or solvent mixtures must have a boiling point above the temperature of the PVC sheet. Thus, a mixture of 1,1,2- trichloroethane (b.pt. 114°C.) and tetrachloroethylene (b.pt. 121°C.) in a weight ratio of between 1.5 and 3 thereof was used. Low boiling solvents, e.g. methylene chloride, (b.pt. 40°C.) and/or dichloroethane (b.pt. 83°C.) would not be suitable for PVC sheets heated to 120°C.

Baumgartel, H. et al, in FRG Patent Applications 28 08 005 and 38 08 036, both filed 2/24/78, laid-open 8/30/79, describes a process for rejuvenating installed, weathered PVC siding by spraying, brushing or roller-coating the siding with a solution of U.V. absorber in an organic solvent or mixture of solvents. The concentration of U.V. stabilizer in such solution was between 0.1 to 5 wt.%, preferably 0.5 to 2.5 wt.%. The preferred solvent system was a mixture of liquids, particularly methylene chloride and a second liquid, such as acetone, ethyl acetate, methyl acetate, THF cyclohexanone, DMF and methyl alcohol.

In summary, the art has not provided a suitable composition for surface modifying a PVC resinous body effectively at ambient temperatures with a predetermined, effective amount of modifier ingredient within a selected contact time without leaving substantial amounts of residual solvent in the treated body or solid modifier on the surface of the treated body.

In particular, it is desired that the U.V. stabilizing composition provide an economically effective, stabilizing amount of U.V. stabilizer incorporated within the surface region of a resin sheet body, in a suitable contact time, while leaving only a minimum and constant amount of solvent in the body which does not affect the planarity of the body.

An economically effective, stabilizing amount of U.V. stabilizer is defined herein as a U.V. stabilized article which affords substantially maximum U.V. protection with a substantially minimum amount of U.V. stabilizer therein, that is, higher amounts of U.V. stabilizer incorporated into the surface region of the article would not materially enhance the U.V. protection obtained at the economically effective, stabilizing amounts of U.V. incorporation.

In addition, to be an economically effective, stabilizing amounts of U.V. stabilizer, it must be incorporated within the PVC siding sheet within the available contact time of the process, as determined by the swelling rate of the solvent, the line speed, e.g. the feed rate PVC residential siding, and the requirement that a reasonable distance of separation be maintained between the application and solution displacement zones in the process.

Furthermore, it is required that the U.V. stabilizing composition provide a surface modified article having only a minimum and constant amount of solvent in the PVC resin after surface modification, which does not affect the physical appearance of the treated article, particularly the planarity of a residential siding sheet.

Finally, the use of U.V. composition should not result in any stabilizer remaining on the surface of the treated sheet.

Accordingly, it is an object of the present invention to provide a U.V. stabilizer composition comprising a U.V. stabilizer dissolved in a resin-swellable, non-flammable, liquid solvent, wherein said composition has a predetermined concentration range of stabilizer which is particularly effective for surface modifying a PVC resin body at ambient temperatures, and without requiring evaporation of solvent, with an economically effective, stabilizing amount of U.V. stabilizer in the surface region thereof, within a selected application time, while minimizing the amount of residual solvent which enters the resin body, and without affecting the appearance of the modified surface, particularly its surface perfection and planarity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood by referring to the following drawings, in which:

Fig. 1 is a graph of change in Yellowness Index ( YI)

2 vs. U.V. stabilizer in g/m incorporated into the surface region of a PVC sheet.

Fig. 2 is a graph of curvature of a surface modified PVC siding sheet, in inches, vs. % retained solvent therein.

Figs. 3a and 3b are surface modified PVC siding articles made using (a) U.V. stabilizer compositions having a low concentration of stabilizer, and (b) UV stabilizer compositions having a concentration of stabilizer within the range of the invention, which shows the effect of solvent upon curvature of the modified article.

Fig. 4 is a plot of wt.% retained solvent in a PVC article vs. concentration in wt.% of U.V. stabilizer in the

2 applying composition, based on 1.8 g/m incorporation into a

35 mil sheet.

2 Fig. 5 is a graph of amount of U.V. stabilizer in g/m incorporated into the surface region of a PVC sheet vs. concentration of U.V. stabilizer in the applying composition using a contact time of 7.5 seconds.

DETAILED DESCRIPTION OF THE INVENTION

In copending patent application Serial No. 945,595, a process is described for producing a U.V. stabilized, surface modified PVC resin body. The U.V. stabilized article is made by a continuous process in which the resin body is contacted with a solution of U.V. stabilizer in a resin-swellable organic solvent. Thereafter, residual stabilizer and solvent are displaced from the modified surface; both steps are carried out under conditions which are non-evaporative of the solvent.

In a preferred embodiment of this process, the resin body is immersed in a suitable liquid media, such as water, and the surface to be modified is contacted through the liquid media with a solution of a UV stabilizer in the resin- swellable organic solvent, and, a jet of water is directed against the modified surface to displace any residual stabilizer and solvent thereon.

The preferred arrangement in this process is a two- layer, two-phase system, where water is the upper layer, and the stabilizer composition is the lower layer. The PVC resin sheet thereby is immersed in the upper layer and the stabilizer composition is pumped from the lower layer and directed onto the sheet surface to be modified. Excess stabilizer solution then falls off the surface of the body by gravity and returns to the lower layer. During the time of application of the stabilizer composition, the solvent mixture in the composition is prevented from evaporating into the atmosphere by the blanket of liquid above it, which is advantageous for producing a modified surface having a high degree of surface perfection, and for ecological reasons.

In operation, a continuous resin strip of extruded polyvinyl chloride is fed onto the upper layer at a predetermined rate from below a roller which is positioned below the surface of the water. In the "application zone" a series of applicator nozzles are oriented below the surface level of the water with their orifices directed towards the surface strip. The applicator nozzles continuously direct a stream of stabilizer composition over the upper surface of the moving resin trip. The thus-applied stabilizer solution remains on the surface of the strip whereupon the surface region is modified effectively with stabilizer.

Downstream of the applicator zone is a "displacement zone", in which residual stabilizer solution is removed in situ from the thus-treated surface of the strip. The term "in situ" means that the displacement step is carried out without exposing the treated surface to the ambient atmosphere; rather, the surface remains under water so that the solvent cannot evaporate.

The duration of passage from the applicator zone to the displacement zone is defined as the "contact time" of the process.

In the displacement zone, a jet element directs a spray of displacing liquid, preferably water, at a pressure sufficient to displace residual stabilizer solution from the treated surface of the strip.

A second roller is located ahead of the displacement zone and below the level of the water to accept the thus- treated resin strip after it leaves the displacement zone. Variable speed nip roller pullers are positioned outside the tank to move the strip at a predetermined speed through and out of the tank.

The preferred solvent is water-immiscible, has a boiling point of less that 85°C, and is non-aggressive towards the resin. Methylene chloride is preferred (b.pt. 40°C).

In order to provide a diffusion process for surface modification of residential PVC siding, for example, it is necessary to provide a U.V. stabilizer composition which will incorporate a predetermined, effective, stabilizing amount of U.V. stabilizer within the surface region of the sheet, i.e. to a depth of up to about 200 microns, without leaving an appreciable amount of solvent in the treated article, or stabilizer on its treated surface, and within a contact time which will allow for reasonable separation of application and displacement zones, particularly in a continuous process.

Referring now to the drawings. Fig. 1 is a plot of weathering data reported as changes in Yellowness Index

(delta YI) vs. the amount of UV stabilizer in g/m present in the surface region of a surface modified PVC siding sheet.

The data shows that economically effective UV protection is

2 achieved when about 1.8-2.8 g/m of the UV stabilizer is present in the surface region. Lower amounts give substantially poorer protection, i.e. the ascending portion of the curve, and higher amounts afford very little improvement in weathering and is economically unjustified.

Accordingly, it is desirable to provide a stabilizer composition which will provide such useful amount of UV material in the surface region.

Fig. 2 is a plot of curvature of the siding article in inches of height from the level vs. wt.% retained solvent in the article after incorporation of the UV stabilizer. For commercial use as a siding material, it is necessary that the siding article be substantially planar. Accordingly, a curvature of greater than 0.3 inches is considered unacceptable for the industry. Less than 0.3 inches of a curvature can be achieved if solvent incorporation is less than 0.7%.

Fig. 3 is a representation of actual siding sheets which have been surface modified by the process described herein. The sheets show (a) acceptable curvature and (b) unacceptable curvatures, that is, below and above 0.3 inches of curvature.

Fig. 4 is a plot of wt.% retained solvent in the PVC siding article after surface modification vs. UV stabilizer concentration in wt.% in the applying composition. The data shows that the desired less than 0.7% retained solvent is achieved at a stabilizer concentration of 18 wt.% or more. Within a stabilizer concentration range of 18-40 wt.%, the amount of retained solvent is about 0.2-0.4 wt.%. This represents a substantially minimum and constant amount where the slope of wt.% solvent vs. stabilizer concentration is substantially zero.

Accordingly, it would be desirable to use this stabilizer concentration to achieve the desired low amount of retained solvent, and thereby the low curvature values.

However, it is necessary that this concentration satisfy the other condition of providing an economically effective amount

2 of 1.8-2.8 g/m of UV stabilizer within the region of the sheet, that is, down to 200 microns from the surface from the surface, and at least 70% of this amount within the first 100 microns from the surface. This degree of incorporation also must be achieved within contact times allowable by the process itself for production of residential PVC siding, that is, a fee rate of 60 ft/sec. and a reasonable separation of applicatic and displacement zones. In practice, a contact time of about 5-10 seconds is required.

Previously, it had been assumed that an increase in concentration of stabilizer in the applying composition would result in a corresponding increase in incorporation UV stabilizer within the surface region of the article. Accordingly, the prior art had believed that the desired economically effective amount of UV stabilizer, i.e. 1.8-2.8 g/m . could not be achieved with a stabilizer concentration of 18-40 wt.%, which provided the required low wt.% retained solvent and thereby, low % curvature in the article, without resorting to such short contact times in the process herein that the distance of separation between the equipment in the application and displacement zones was unreasonably short.

The graph in Fig. 5 shows that, unexpectedly, the amount of UV stabilizer incorporated into the surface region of the article increases with stabilizer concentration in the applying composition only for dilute solutions, that is, below 18 wt.% stabilizer. Thereafter, the amount of UV stabilizer incorporated into the article actually decreases with concentration, i.e. the relationship of amount of UV stabilizer incorporated vs. concentration has a negative slope for compositions having a stabilizer concentration of greater than 18 wt.%.

Accordingly, this discovery enables the use of high concentrations of stabilizer in the applying solution to achieve all of the following parameters simultaneously,

2 namely (1) the desired 1.8-2.8 g/m of stabilizer incorporation, (2) the required value of less than 0.7 wt.% retained solvent in the treated sheet, resulting in low curvature, and (3) the use of a contact time of 5-10 seconds while producing residential siding at a feed rate of 60 ft/second in the two-phase process.

More particularly. Fig. 5 shows that only an 18-40 wt.% stabilizer composition will achieve the desired amount of

2 incorporation of 1.8 g/m within a contact time of 7.5 seconds, and leave less than 0.7% solvent therein. A concentration of less than 18 wt.%, or greater than 40 wt.% stabilizer, in the composition cannot provide these necessary results.

Claims

WHAT IS CLAIMED IS;

1. A U.V. stabilizer composition for surface modification of a PVC resinous body with an economically effective, stabilizing amount of a U.V. stabilizer within a predetermined contact time while leaving only a substantially minimum and constant amount of solvent therein which comprises: a U.V. stabilizer dissolved in a PVC resin- swellable organic solvent having a stabilizer concentration within a range wherein:

(a) the slope of the relationship of amount of stabilizer incorporated into said body vs. stabilizer concentration is negative, and

(b) the slope of the relationship of amount of solvent which enters the body vs. stabilizer concentration is substantially zero.

2. A U.V. stabilizer composition according to claim 1 wherein said solvent is methylene chloride.

3. A U.V. stabilizer composition according to claim 1 wherein said U.V. stabilizer is present at a concentration of at least about 18% by wt. of said composition.

4. A U.V. stabilizer composition according to claim 1 wherein said U.V. stabilizer is present at a concentration of about 18-40% by wt. of said composition.

5. A U.V. stabilizer composition according to claim 1 wherein said solvent is non-aggressive towards said resin, is water-immiscible, and has a boiling point of less than about 85°C.

6. A U.V. stabilizer composition according to claim 5 wherein said solvent has a boiling point of about 40°C.

7. A U.V. stabilizer composition for surface modification of a PVC resinous body with an economically effective, stabilizing amount of a UV stabilizer comprising about 18-40% by wt. of a U.V. stabilizer dissolved in a PVC resin-swellable organic solvent.

8. A U.V. stabilizer composition according to claim 7 wherein said solvent is methylene chloride.